It is known in the prior art to use an elongated, multiple-segment capacitance probe for determining the volume of fuel in an underground fuel storage tank. One such system is described in U.S. Pat. No. 4,349,882, which teaches a method and apparatus for determining liquid level and volume of fuel in a storage tank through use of such a probe. U.S. Pat. No. 3,777,257 also describes measuring apparatus incorporating a capacitance probe for measuring the volume of fuel within a tank. The above-identified patents are representative of systems available for replacing a conventional measuring stick approach for determining the liquid level interface and volume of fuel in an underground storage tank.
An improved capacitance probe structure has also been described in copending application entitled "Liquid Level and Volume Measuring Method and Apparatus", Ser. No. 517,590, filed July 27, 1983, and assigned to the assignee of the present application. This copending application describes an elongated, multiple-segment capacitance probe for use in a measuring system for locating a liquid level interface. The probe includes a support having an elongated center section as one plate of a plurality of capacitors. A first plurality of flat capacitor plates is mounted in a spaced apart overlapping arrangement to the center section of the support along the longitudinal axis thereof and parallel therewith. A second plurality of flat capacitor plates is also mounted in a spaced apart overlapping arrangement to the center section of the support along the longitudinal axis thereof and in a position opposite and displaced from the first plurality of capacitor plates. Each of the capacitor plates comprises an individual capacitor with the center section of the support.
Although the multiple segment capacitance probe structure described in the above-identified application has proved advantageous for determining the liquid level interface within a tank, it is has now been found that this overlapping capacitor structure is not required to precisely determine this interface. Accordingly, the present invention describes an improved capacitance probe structure for use in a measuring system for location of a liquid level interface in an underground storage tank.